Dijkstra.java

02. Algorithms/05. Graphs/04. Dijkstra/Dijkstra.java

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+//Implementation of dijkstra's algorithm in Java using priority queue
+
+import java.util.*;
+
+class Dijkstra {
+    static class Edge {
+        int vertex, weight;
+        Edge(int v, int w) {
+            vertex = v;
+            weight = w;
+        }
+    }
+
+    static class Graph {
+        int V;
+        LinkedList<Edge>[] adj;
+
+        Graph(int V) {
+            this.V = V;
+            adj = new LinkedList[V];
+            for (int i = 0; i < V; i++) {
+                adj[i] = new LinkedList<>();
+            }
+        }
+
+        void addEdge(int u, int v, int weight) {
+            adj[u].add(new Edge(v, weight));
+            adj[v].add(new Edge(u, weight));
+        }
+
+        void shortestPath(int src) {
+            PriorityQueue<Edge> pq = new PriorityQueue<>(V, Comparator.comparingInt(edge -> edge.weight));
+            int[] dist = new int[V];
+            Arrays.fill(dist, Integer.MAX_VALUE);
+            pq.add(new Edge(src, 0));
+            dist[src] = 0;
+
+            while (!pq.isEmpty()) {
+                Edge edge = pq.poll();
+                int u = edge.vertex;
+
+                for (Edge e : adj[u]) {
+                    int v = e.vertex;
+                    int weight = e.weight;
+
+                    if (dist[v] > dist[u] + weight) {
+                        dist[v] = dist[u] + weight;
+                        pq.add(new Edge(v, dist[v]));
+                    }
+                }
+            }
+
+            System.out.println("Vertex Distance from Source");
+            for (int i = 0; i < V; i++) {
+                System.out.println(i + " \t\t " + dist[i]);
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        int V = 9;
+        Graph g = new Graph(V);
+
+        g.addEdge(0, 1, 4);
+        g.addEdge(0, 7, 8);
+        g.addEdge(1, 2, 8);
+        g.addEdge(1, 7, 11);
+        g.addEdge(2, 3, 7);
+        g.addEdge(2, 8, 2);
+        g.addEdge(2, 5, 4);
+        g.addEdge(3, 4, 9);
+        g.addEdge(3, 5, 14);
+        g.addEdge(4, 5, 10);
+        g.addEdge(5, 6, 2);
+        g.addEdge(6, 7, 1);
+        g.addEdge(6, 8, 6);
+        g.addEdge(7, 8, 7);
+
+        g.shortestPath(0);
+    }
+}